The unhurried fashion in which James VI of Scotland ambled south towards London to claim his crown in 1603, stopping off to hunt along the way and arriving six weeks after Elizabeth I died, suggests there was nothing terribly dramatic about the event. The man who would be James I of England, the first Stuart monarch, was certainly in no big rush.

Yet this was the end of the Tudor dynasty, one of our longest-held historical obsessions. And it was the seed of the union between Scotland and England – the creation of a political Great Britain that will survive, well, at least until next year's referendum on Scottish independence. James's coolness seems almost mocking in the face of our own excitement.

The Tudor period between 1485 and 1603 brought cultural, religious and political revolution. But our fixation with the era has as much, if not more, to do with the vibrant individual stories it presents as with the family's debatable self-image as a dynasty. Exuberant Henry VIII with his six wives, "Bloody" Mary and Elizabeth I, aka Gloriana, all provide compelling narratives. Even dark, grim Henry VII – the Brittany-based man who started it all – has come back into the limelight. Many supporting players also boast dramatic stories – be they power-brokers like Cromwell and Wolsey or bold but unfortunate women such as Catherine of Aragon, Anne Boleyn and Mary Queen of Scots. We should not be surprised that the Tudors provide us with such great fictional television fodder and fine historical biographies while inspiring novelists like Hilary Mantel – not to mention giving us shelves full of romantic mush. We cannot get enough of them.

Two bold new histories widen the focus, adding context and meaning. In Tudor: The Family Story, Leanda de Lisle explains both where the Tudors came from and where they got to, starting with a cheeky Welsh squire called Owen. In Crown of Thistles, Linda Porter tells the backstories of England and Scotland as they head towards a union which we often assume was inevitable.

There was nothing inevitable, however, about James I of England. Porter's magnificent account of Scotland's feuding factions makes that clear – even if the battles were more to control monarchs, especially in a country that crowned several before their second birthdays, than to replace them. In Porter's account, indeed, one of the rare unifying forces was England itself. Faced with a chance to bloody the old enemy, Scotland would (more or less) pull together. French money, meanwhile, encouraged it to maintain the "Auld Alliance" against England.

The great Scottish tragedy is that its army kept on losing. From Flodden Field and Solway Moss to the "Black Saturday" at Pinkie, the darkest moments of Scottish history are on the battlefield against the English foe. When little James V was crowned shortly after Flodden (where his father died), it became known as the Mourning Coronation, such was the death toll. Porter analyses these battles wonderfully and does not spare us the brutality of the ensuing routs. English victories, however, did not bring union by force. English monarchs were too stretched or too wary to press home their advantage.

Scottish monarchs outdid their English rivals in the bedroom, filling their nurseries with children (legitimate and illegitimate) while the Tudors fretted about the siring – or choosing – of just one suitable heir. A son bolstered the monarch against rivals, be they of royal blood or impostors like Perkin Warbeck. A daughter was less of a guarantee. But Tudor boys were scarce. This explains Henry VII's tight control of young prince Henry as well as the latter's penchant for divorce and beheading. Elizabeth I, meanwhile, refused to name successors who, in the absence of children of her own, could only become rivals.

De Lisle's family history also goes beyond England, this time to Wales – the birthplace of Owen ap Maredudd ap Tudur who, ironically, was able to marry a royal because he was only a modest, if charming, squire. That made him a suitably unthreatening second husband for Henry V's widow, Catherine of Valois. It was his grandson, born to 13-year-old Margaret Beaufort, who became Henry VII. This may seem familiar territory, but De Lisle's masterful command of the facts – great and small – provides a complete and entertaining overview.

Marriages as often caused problems as not. They sealed alliances between countries or families. A wrong call or, even, an attempt to marry for love, could bring disastrous consequences. Women, through whose stories we increasingly view 16th-century history, needed to take special care – when permitted to choose for themselves. Perhaps the most unfortunate was Mary Queen of Scots. Her brief period as queen consort in France ended with Francis II's early death. She then married the vain and self-serving Lord Darnley, only to see him murdered before she was raped and forced into marriage by the Earl of Bothwell. Her escape from that was into effective imprisonment in England, where Elizabeth saw her as a dangerous rival. She was easily trapped in a treason plot and beheaded.

Yet this was an extraordinary century for women as rulers, be they regents or queens regnant. Beyond Isabella of Castile, whose joint monarchy with Ferdinand of Aragon the previous century had been so successful, there were few models to follow. Both England and Scotland struggled to come to terms with the idea. Men feared women's uncontrolled passions and sexual incontinence. They rued their lack of martial vigour. More than anything else, though, they feared other men controlling women rulers. The Scottish protestant firebrand John Knox, author of a polemic against "the monstrous regiment of women", was among the most vocal critics.

In the background, the religious revolution sparked by Martin Luther and other opponents of the Roman church rumbled on. Scotland's story is of religious change demanded from below the monarchy. It is a reminder that England may not have needed Henry's divorce from Catherine of Aragon – and insistence on marrying Anne Boleyn – to produce a split with Rome.

The big picture provided by De Lisle shows Tudor insecurity revolving around the thorny issue of succession. Porter's valuable review of the path towards union proves there was nothing predestined, or particularly preplanned, about the coming together of Scotland and England.

The man really to blame was Henry VII, who set up the possibility by marrying his daughter Margaret to Scotland's James IV. He was sanguine about a Scottish descendent eventually becoming monarch in England. In the end, he predicted, it would be England that dominated. He was right. James VI of Scotland, who was that descendent, seemed equally relaxed.